MPI_Send(100): Invalid rank has value 1 but must be nonnegative and less than 1

问题

I am learning MPI in python by myself. I just started from the basic documentation of MPI4py. I started with this code:

from mpi4py import MPI

comm = MPI.COMM_WORLD
rank = comm.Get_rank()

if rank == 0:
   data = {'a': 7, 'b': 3.14}
   comm.send(data, dest=1, tag=11)
elif rank == 1:
   data = comm.recv(source=0, tag=11)

When I ran this program, I got following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "MPI/Comm.pyx", line 1175, in mpi4py.MPI.Comm.send (src/mpi4py.MPI.c:106424)
  File "MPI/msgpickle.pxi", line 211, in mpi4py.MPI.PyMPI_send (src/mpi4py.MPI.c:42120)
mpi4py.MPI.Exception: Invalid rank, error stack:
MPI_Send(174): MPI_Send(buf=0x10e137554, count=25, MPI_BYTE, dest=1, tag=11, MPI_COMM_WORLD) failed
MPI_Send(100): Invalid rank has value 1 but must be nonnegative and less than 1

I didn't find any working solution for this problem. I am using Mac OS X El Capitan.

Thanks in Advance!

回答1:

The program complains that 1 is not a valid rank for MPI_Send(): it means that your program is running on a single process.

Are you running it by using python main.py ? Try to use mpirun -np 2 python main.py, where 2 is the number of processes. The latter is the usual way to run mpi programs.

来源：https://stackoverflow.com/questions/35669614/mpi-send100-invalid-rank-has-value-1-but-must-be-nonnegative-and-less-than-1